http://astrobob.areavoices.com/?blog=78068 wrote:
Mars shines brightest this weekend
Posted on March 2, 2012 by astrobob
<<If Mars has been catching your attention lately, it’s because the planet is now the brightest it’s been in nearly two years. Easy to see in the eastern sky, Mars comes to opposition tomorrow, rising at sunset and remaining visible the entire night. We look out in one direction to see Mars (east) and in exactly the opposite direction to face the sun. You can literally feel these two opposing worlds by stepping outside during evening twilight. As the sunset glow fades in the southwest, Mars lifts its red face in the opposite corner of the sky.
Because the two planets are together on the same side of the sun, they’re also closest. Mars is nearest Earth on the 5th at a distance of 67.7 million miles. Its average distance is nearly three times farther. The current close approach means that the planet is nearly as bright as Sirius and shows a larger than normal disk through a telescope. That’s good news for Mars lovers, who are passionate followers of the planet’s wispy clouds, shrinking north polar cap and occasional dust storms.
As oppositions go, this is one of the most distant. If both planets’ orbits were perfect circles, oppositions would all be equally close, but because Mars’ orbit is more elliptical than Earth’s, the distance between the two planets varies at each opposition. The 2012 opposition is called aphelic (ap-HEE-lik) because Mars is near its greatest distance from the sun at the same time it lines up with Earth. During a perihelic opposition, Mars is closest to the sun and hence closer to the Earth.
The difference between oppositions can be dramatic. During the last perihelic one in August 2003, Mars was 34.6 million miles away, nearly twice as close as it will be this weekend. Back then it shone brighter than Jupiter with a disk that spanned 25 arc seconds compared to this season’s 13.9 seconds. Mars goes through a complete cycle of close to far oppositions every 15.8 years. Tomorrow’s opposition is nearly identical to the one in 1995. The next perihelic approach will be July 27, 2018.
With the naked eye, you can enjoy the bright, fiery red-orange color of the planet and watch as it moves west in retrograde motion toward Leo’s brightest star Regulus. A small telescope will show vague dark markings and the tiny north polar cap. It’s late spring in Mars’ northern hemisphere and the cap has been shrinking rapidly the past few weeks as the sun’s heat causes it to vaporize. Meanwhile, the southern polar cap, tipped over the limb and currently not visible, has been expanding during the Marian fall. The cap grows under a vast hood of clouds called the South Polar Hood that keen-eyed observers can see as a pale arc along the planet’s southern edge.>>